Here are four figures from our collection at Silver Creek, May 31, 2003. Six pools were sampled, 2 above the waterfall, and the first four larger pools with fish below the falls (over about half a mile). Sampling effort was very uneven above and below the waterfall. Above the fall, only two seine hauls per pool were made (4 total). Below the falls sampling was more intense with usually two complete passes with an electrofisher and between two and four passes with a 15 ft seine.
Below the waterfall, pools were numbered in a downstream sequence. The first pool was heavily angled by four of us in 1999 with nearly 200 Lepomis cyanellus removed. A number of sunfish were also removed from pool 2 in 1999 and 2001, but it only represented a minor portion of the population within that pool. Pool 1 had a very dense growth of nitella and the water level was relatively low. The second pool had a good growth of nitella around its perimeter. The lower two pools lacked any aquatic vegetation.
Gila intermedia size classes by pool.
Gila intermedia size classes for pools above and below the waterfall combined.
The average size of Gila intermedia above the falls was 71.2 mm (N = 163), below the falls it was 112.7 (N = 23). The average above the falls would have been much lower if we had included all the chubs that were <20 mm that we did not measure (to avoid killing them).
Lepomis cyanellus size classes by pool.
Lepomis cyanellus size classes for all pools combined.
The number of L. cyanellus from each pool was: pool 1 = 69 (plus 49 unmeasured), pool 2 = 67, pool 3 = 44, and pool 4 = 21 (with about 10 more fish not measured).
Only one other species was collected, two adult Pantosteus clarkii from pool 3. Other species previously recorded include Agosia chrysogaster and Pimephales promelas.
Interestingly, in pool 1 the size classes of Lepomis cyanellus were skewed to relatively smaller fish, within only a few relatively large fish being present. Presumably this is due to their mass removal in 1999, although this seems like a very long time lag for recruitment not to fill in the missing size classes. The presence of large numbers of very small (<20 mm) L. cyanellus in pool 2 seems attributable to the dense cover of nitella around the pools margins.
Interestingly, both species tend to show a similar over distribution of size class when the data are combined. Both tend to have large numbers of the smallest two size classes with a substantial dip, followed by a more normal distribution with the bulk of the population consisting of medium sized fish.
